During the early development of D. melanogaster a single egg cell is converted into a multicellular organism (the first instar larva) which contains in a defined spatial arrangement a variety of specialize organs, tissues, and cell types. The steps in embryogenesis of D. melanogaster include: differential cell divisions, cellular movements, the establishment of cell-cell interactions, and the formation f specialized tissues and cell types. The research described in this proposal will focus on one aspect of embryogenesis which is particularly amenable to study in D. melanogaster - the role of, and the mechanisms controlling differential gene expression during embyrogenesis. Two questions are of special interest: 1. Is there a temporal coordination between a "program" of gene expression and the differentiation of specific tissues or cell types during embryogenesis? and 2. If so what are the mechanisms involved that result in coordinate gene expression?